As compared with an electrode for a phosphoric acid fuel cell, an electrode for a solid polymer electrolyte fuel cell is required to have gas diffusion-permeability, strength to be durable to handling, flexibility, strength to stand the compression at the time of electrode production and electrode assembly, and the like. Further, since the solid polymer electrolyte fuel cell is required to be small in size, as compared with a phosphoric acid fuel cell, the electrode for it is also required to be thin. As the electrode for such a solid polymer electrolyte fuel cell, mainly used are those which are produced by forming paper from carbon short fibers, impregnating the paper with a thermosetting resin, curing the resin, and then carbonizing the resultant paper, and in order to improve the productivity of a fuel cell, the electrode has to be flexible enough to be rolled in a roll. However, many electrodes ever made available are thick and mostly easily broken when being bent. Further, since those conventional electrodes have a few contacting points of carbon fibers, they have a problem that the conductivity becomes worse if the porosity is increased.
A porous carbon electrode substrate provided with an improved conductivity by mixing carbonaceous milled fibers is described in Japanese Patent Laid-Open No. 142068/1995, however the substrate is too thick in thickness and thus insufficient in flexibility to be used for a solid polymer electrolyte fuel cell.
Invention of a porous carbon plate and its production method is described in Japanese Patent Laid-Open No. 157052/1997, the electrode of the invention has a low bulk density and therefore it cannot be said that the conductivity of the electrode is sufficient.